<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
</head>
<body>
<p>Click the button to wait 3 seconds, then alert "Hello".</p>

<button onclick="myFunction()">Try it</button>

<script>
    function myFunction() {
        setTimeout(function(){ alert("Hello"); }, 3000);
    }
</script>
</body>
</html>